| Section T | T index | 541-549 of 589 terms |
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turbopause—The surface that separates the homosphere, in which the constituents of the atmosphere are well mixed by turbulence, from the heterosphere, in which constituents adopt their individual distributions with height as the result of molecular diffusion. The turbopause is not very clearly marked, but usually lies at a height of about 100 km, near the base of the thermosphere.
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turbulence closure—The problem in turbulence analysis that occurs when Reynolds averaging is applied to Navier–Stokes equations; the result is that there are more unknowns than equations. In order to solve the problem, assumptions have to be made concerning the unknown quantities in the equations. These unknowns appear as correlations between the fluctuating quantities. The simplest closure is the so-called K theory. A more advanced form is the direct interaction approximation.
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turbulence intensity—The ratio of the root-mean-square of the eddy velocity to the mean wind speed. In general, it is a quantity that characterizes the intensity of gusts in the airflow.
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turbulence kinetic energy—(Abbreviated TKE.) The mean kinetic energy per unit mass associated with eddies in turbulent flow. A budget equation for TKE can be formed from the Navier–Stokes equations for incompressible fluid flow through Reynolds decomposition and Reynolds averaging. For most meteorological applications it is assumed that buoyancy effects are in the z direction only, that the mean vertical velocity is zero (hydrostatic scaling), and that molecular diffusion is neglected. See also hydrostatic balance, isotropic turbulence, local isotropy, Reynolds number, Reynolds stresses, turbulence length scales, turbulence spectrum, viscous fluid.
Hinze, J. O., 1975: Turbulence, 2d ed., McGraw–Hill, 790 pp.
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turbulence length scales—Measures of the eddy scale sizes in turbulent flow. The separation between the largest and smallest sizes is determined by the Reynolds number. The largest length scales are usually imposed by the flow geometry, for example, the boundary layer depth. Because turbulence kinetic energy is extracted from the mean flow at the largest scales, they are often referred to as the “energy-containing” range. The smallest scales are set by the viscosity and the rate at which energy is supplied by the largest-scale eddies. Intermediate between these scales are the inertial subrange scales for which turbulence kinetic energy is neither generated nor destroyed but is transferred from larger to smaller scales. Smaller-scale eddies are generated from the larger eddies through the nonlinear process of vortex stretching. Typically, energy is transferred from the largest eddies to the smallest ones on a timescale of about one large- eddy turnover. There are standard turbulence length scales for each of the eddy scale sizes; integral length scales for the energy-containing eddies, Taylor microscale for the inertial subrange eddies, and Kolmogorov microscale for the dissipation range eddies.
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